'\" t
.\"     Title: ALTER INDEX
.\"    Author: The PostgreSQL Global Development Group
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: 2021
.\"    Manual: PostgreSQL 13.3 Documentation
.\"    Source: PostgreSQL 13.3
.\"  Language: English
.\"
.TH "ALTER INDEX" "7" "2021" "PostgreSQL 13.3" "PostgreSQL 13.3 Documentation"
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.SH "NAME"
ALTER_INDEX \- change the definition of an index
.SH "SYNOPSIS"
.sp
.nf
ALTER INDEX [ IF EXISTS ] \fIname\fR RENAME TO \fInew_name\fR
ALTER INDEX [ IF EXISTS ] \fIname\fR SET TABLESPACE \fItablespace_name\fR
ALTER INDEX \fIname\fR ATTACH PARTITION \fIindex_name\fR
ALTER INDEX \fIname\fR [ NO ] DEPENDS ON EXTENSION \fIextension_name\fR
ALTER INDEX [ IF EXISTS ] \fIname\fR SET ( \fIstorage_parameter\fR [= \fIvalue\fR] [, \&.\&.\&. ] )
ALTER INDEX [ IF EXISTS ] \fIname\fR RESET ( \fIstorage_parameter\fR [, \&.\&.\&. ] )
ALTER INDEX [ IF EXISTS ] \fIname\fR ALTER [ COLUMN ] \fIcolumn_number\fR
    SET STATISTICS \fIinteger\fR
ALTER INDEX ALL IN TABLESPACE \fIname\fR [ OWNED BY \fIrole_name\fR [, \&.\&.\&. ] ]
    SET TABLESPACE \fInew_tablespace\fR [ NOWAIT ]
.fi
.SH "DESCRIPTION"
.PP
\fBALTER INDEX\fR
changes the definition of an existing index\&. There are several subforms described below\&. Note that the lock level required may differ for each subform\&. An
ACCESS EXCLUSIVE
lock is held unless explicitly noted\&. When multiple subcommands are listed, the lock held will be the strictest one required from any subcommand\&.
.PP
RENAME
.RS 4
The
RENAME
form changes the name of the index\&. If the index is associated with a table constraint (either
UNIQUE,
PRIMARY KEY, or
EXCLUDE), the constraint is renamed as well\&. There is no effect on the stored data\&.
.sp
Renaming an index acquires a
SHARE UPDATE EXCLUSIVE
lock\&.
.RE
.PP
SET TABLESPACE
.RS 4
This form changes the index\*(Aqs tablespace to the specified tablespace and moves the data file(s) associated with the index to the new tablespace\&. To change the tablespace of an index, you must own the index and have
CREATE
privilege on the new tablespace\&. All indexes in the current database in a tablespace can be moved by using the
ALL IN TABLESPACE
form, which will lock all indexes to be moved and then move each one\&. This form also supports
OWNED BY, which will only move indexes owned by the roles specified\&. If the
NOWAIT
option is specified then the command will fail if it is unable to acquire all of the locks required immediately\&. Note that system catalogs will not be moved by this command, use
\fBALTER DATABASE\fR
or explicit
\fBALTER INDEX\fR
invocations instead if desired\&. See also
CREATE TABLESPACE (\fBCREATE_TABLESPACE\fR(7))\&.
.RE
.PP
ATTACH PARTITION
.RS 4
Causes the named index to become attached to the altered index\&. The named index must be on a partition of the table containing the index being altered, and have an equivalent definition\&. An attached index cannot be dropped by itself, and will automatically be dropped if its parent index is dropped\&.
.RE
.PP
DEPENDS ON EXTENSION \fIextension_name\fR
.br
NO DEPENDS ON EXTENSION \fIextension_name\fR
.RS 4
This form marks the index as dependent on the extension, or no longer dependent on that extension if
NO
is specified\&. An index that\*(Aqs marked as dependent on an extension is automatically dropped when the extension is dropped\&.
.RE
.PP
SET ( \fIstorage_parameter\fR [= \fIvalue\fR] [, \&.\&.\&. ] )
.RS 4
This form changes one or more index\-method\-specific storage parameters for the index\&. See
CREATE INDEX (\fBCREATE_INDEX\fR(7))
for details on the available parameters\&. Note that the index contents will not be modified immediately by this command; depending on the parameter you might need to rebuild the index with
\fBREINDEX\fR(7)
to get the desired effects\&.
.RE
.PP
RESET ( \fIstorage_parameter\fR [, \&.\&.\&. ] )
.RS 4
This form resets one or more index\-method\-specific storage parameters to their defaults\&. As with
SET, a
REINDEX
might be needed to update the index entirely\&.
.RE
.PP
ALTER [ COLUMN ] \fIcolumn_number\fR SET STATISTICS \fIinteger\fR
.RS 4
This form sets the per\-column statistics\-gathering target for subsequent
\fBANALYZE\fR(7)
operations, though can be used only on index columns that are defined as an expression\&. Since expressions lack a unique name, we refer to them using the ordinal number of the index column\&. The target can be set in the range 0 to 10000; alternatively, set it to \-1 to revert to using the system default statistics target (default_statistics_target)\&. For more information on the use of statistics by the
PostgreSQL
query planner, refer to
Section\ \&14.2\&.
.RE
.SH "PARAMETERS"
.PP
IF EXISTS
.RS 4
Do not throw an error if the index does not exist\&. A notice is issued in this case\&.
.RE
.PP
\fIcolumn_number\fR
.RS 4
The ordinal number refers to the ordinal (left\-to\-right) position of the index column\&.
.RE
.PP
\fIname\fR
.RS 4
The name (possibly schema\-qualified) of an existing index to alter\&.
.RE
.PP
\fInew_name\fR
.RS 4
The new name for the index\&.
.RE
.PP
\fItablespace_name\fR
.RS 4
The tablespace to which the index will be moved\&.
.RE
.PP
\fIextension_name\fR
.RS 4
The name of the extension that the index is to depend on\&.
.RE
.PP
\fIstorage_parameter\fR
.RS 4
The name of an index\-method\-specific storage parameter\&.
.RE
.PP
\fIvalue\fR
.RS 4
The new value for an index\-method\-specific storage parameter\&. This might be a number or a word depending on the parameter\&.
.RE
.SH "NOTES"
.PP
These operations are also possible using
ALTER TABLE (\fBALTER_TABLE\fR(7))\&.
\fBALTER INDEX\fR
is in fact just an alias for the forms of
\fBALTER TABLE\fR
that apply to indexes\&.
.PP
There was formerly an
\fBALTER INDEX OWNER\fR
variant, but this is now ignored (with a warning)\&. An index cannot have an owner different from its table\*(Aqs owner\&. Changing the table\*(Aqs owner automatically changes the index as well\&.
.PP
Changing any part of a system catalog index is not permitted\&.
.SH "EXAMPLES"
.PP
To rename an existing index:
.sp
.if n \{\
.RS 4
.\}
.nf
ALTER INDEX distributors RENAME TO suppliers;
.fi
.if n \{\
.RE
.\}
.PP
To move an index to a different tablespace:
.sp
.if n \{\
.RS 4
.\}
.nf
ALTER INDEX distributors SET TABLESPACE fasttablespace;
.fi
.if n \{\
.RE
.\}
.PP
To change an index\*(Aqs fill factor (assuming that the index method supports it):
.sp
.if n \{\
.RS 4
.\}
.nf
ALTER INDEX distributors SET (fillfactor = 75);
REINDEX INDEX distributors;
.fi
.if n \{\
.RE
.\}
.PP
Set the statistics\-gathering target for an expression index:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE INDEX coord_idx ON measured (x, y, (z + t));
ALTER INDEX coord_idx ALTER COLUMN 3 SET STATISTICS 1000;
.fi
.if n \{\
.RE
.\}
.SH "COMPATIBILITY"
.PP
\fBALTER INDEX\fR
is a
PostgreSQL
extension\&.
.SH "SEE ALSO"
CREATE INDEX (\fBCREATE_INDEX\fR(7)), \fBREINDEX\fR(7)
